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At least 19 recordsLinked to original sources

PubMed1992

Planar motion permits perception of metric structure in stereopsis.

A fundamental problem in the study of spatial perception concerns whether and how vision might acquire information about the metric structure of surfaces in three-dimensional space from motion and from stereopsis. Theoretical analyses have indicated that stereoscopic perceptions of metric relations in depth require additional information about egocentric viewing distance; and recent experiments by James Todd and his colleagues have indicated that vision acquires only affine but not metric structure from motion--that is, spatial relations ambiguous with regard to scale in depth. The purpose of the present study was to determine whether the metric shape of planar stereoscopic forms might be perceived from congruence under planar rotation. In Experiment 1, observers discriminated between similar planar shapes (ellipses) rotating in a plane with varying slant from the frontal-parallel plane. Experimental conditions varied the presence versus absence of binocular disparities, magnification of the disparity scale, and moving versus stationary patterns. Shape discriminations were accurate in all conditions with moving patterns and were near chance in conditions with stationary patterns; neither the presence nor the magnification of binocular disparities had any reliable effect. In Experiment 2, accuracy decreased as the range of rotation decreased from 80 degrees to 10 degrees. In Experiment 3, small deviations from planarity of the motion produced large decrements in accuracy. In contrast with the critical role of motion in shape discrimination, motion hindered discriminations of the binocular disparity scale in Experiment 4. In general, planar motion provides an intrinsic metric scale that is independent of slant in depth and of the scale of binocular disparities. Vision is sensitive to this intrinsic optical metric.

Adult↗

PubMed1992

Vertical disparity and binocular vision in the praying mantis.

We have investigated how the binocular control of prey capture in the praying mantis is affected by abnormally large vertical disparities, which were introduced by prisms placed in front of the eyes. The position of a target on the two retinae determines both the magnitude of head saccades made to fixate a target and its perceived distance. Over the whole range of vertical disparities tested (up to at least 30 deg), the frequency of fixating saccades is normal while the amplitude of their vertical component is a compromise between the saccades specified by each eye individually. Distance measurements are not affected by imposed vertical disparities. But the larger the vertical disparity, the more reluctant the mantid is to strike at the target until disparities exceed 15 deg when no strikes are elicited at all.

Animals↗

PubMed1990

Real world occlusion constraints and binocular rivalry.

A surface occluding a more distant surface gives rise to interocularly unpaired regions to its immediate left and right. The unpaired region on the left side is visible only to the left eye, whereas that on the right side is visible only to the right eye. Thus for real world scenes there are opto-geometrical constraints which determine whether particular combinations of relative depth and right-eye-only or left-eye-only stimuli are ecologically valid or invalid. We report a demonstration and experiments to show that opto-geometrically "valid" unpaired regions are seen as continuous with the rear plane and escape interocular suppression, whereas "invalid" unpaired regions are perceived as closer and are suppressed vigorously. An additional experiment indicates that the results cannot be understood in terms of correspondence solving, but require neural mechanisms that embody real-world occlusion constraints. These results suggest a rather close interaction between stereopsis and rivalry "modules". Since explicit eye-of-origin information is lost relatively early in the hierarchical organization of cortical visual processing, we argue that occlusion-related constraints must be embodied at such early levels.

Chi-Square Distribution↗

PubMed1990

da Vinci stereopsis: depth and subjective occluding contours from unpaired image points.

Distant surfaces are occluded by nearer surfaces to different extents in the two eyes, leading to the existence of unpaired image points visible in one eye and not the other. An ecological analysis of the real world situation that could have given rise to such unpaired points indicates the presence of a depth constraint zone, defined by visibility lines between which possible real world points must lie. The leading edge of this zone starts at the edge of a fused binocular occluding surface and recedes linearly with increases in horizontal distance to the unpaired point. Psychophysical evidence indicates that the human visual system makes use of this unpaired information in a remarkably adaptive manner, showing an increase in perceived depth for increasing horizontal separations between the unpaired target and fused edge, at least over a significant angular range (approx. 25-40 min arc). We also show that unpaired points in binocular images can lead to the formation of subjective occluding contours and surface having the qualitatively appropriate sign of depth. Furthermore, we show that the visual system could not recover depth of unpaired points camouflaged from the other eye against silhouettes. Our findings indicate that the visual system makes use of occlusive relations in the real world to recover depth, contour, and surface from unpaired points. The fact that such processes must utilize eye-of-origin information implies that they share this essential characteristic with classical or Wheatstone stereopsis. The necessity of eye-of-origin information also suggests that the processing may begin relatively early in cortical visual processing, possibly as early as V1. Finally, the novel emergence of subjective occluding contours from unpaired monocular stimuli raises the possibility that this process is mediated by visual experience, built up by the association of unpaired points and occluding contours.

Depth Perception↗

PubMed1991

On the coexistence of stereopsis and binocular rivalry.

Dichoptically viewed complex texture stereograms with correlated spatial frequency information can yield stable depth perception, implying cooperative interaction between the two eyes. Dichoptically viewed dissimilar texture pairs may yield competition in the form of binocular rivalry. To study whether stereopsis and rivalry can spatially coexist when stimulus conditions for both are present, we had observers dichoptically view spatial frequency filtered random-dot patterns. The left eye viewed one half-image of an RDS; the right eye viewed the superimposition of the other RDS half-image (which when paired alone with the left-eye RDS yielded stereoscopic depth) and a noise target (which on its own engaged in rivalry with the right eye target). Observers judged the quality of depth and the rate of rivalry for these stereo-pairs. When the contrast of the noise component was low, observers experienced stereopsis and stable single vision that included the noise. At intermediate noise contrasts, local regions were seen either in rivalry or in stereoscopic depth, but rivalry and depth were not experienced at the same spatial location simultaneously. At high noise contrasts, the right eye target dominated almost exclusively, with little hint of stereopsis. Essentially the same pattern of results was obtained in forced-choice experiments in which observers judged the direction of stereoscopic tilt from vertical cosine gratings differing slightly in spatial frequency. Considered together, these results are inconsistent with theories positing that rivalry and stereopsis coexist at the same spatial location because they occur within independent, parallel pathways.

Depth Perception↗

PubMed1992

Orientation dependence in the recognition of familiar and novel views of three-dimensional objects.

We report four experiments that investigated the representation of novel three-dimensional (3D) objects by the human visual system. In the first experiment, canonical views were demonstrated for novel objects seen equally often from all test viewpoints. The next two experiments showed that the canonical views persisted under repeated testing, and in the presence of a variety of depth cues, including binocular stereo. The fourth experiment probed the ability of subjects to generalize recognition to unfamiliar views of objects previously seen at a limited range of attitudes. Both mono and stereo conditions yielded the same increase in the error rate with misorientation relative to the training attitude. Taken together, these results support the notion that 3D objects are represented by multiple specific views, possibly augmented by partial viewer-centered 3D information.

Computer Simulation↗

PubMed1992

Aniseikonia and stereoacuity in pseudophakic patients. Unilateral and bilateral cases.

PURPOSE: To evaluate the efficacy of intraocular lens (IOL) implant procedures, analyzing visual function of the operated eyes and the resulting binocular vision. METHOD: The authors measured aniseikonia and stereoacuity in patients with both bilateral and unilateral posterior chamber intraocular lenses (PC IOLs). The aniseikonia was measured with the New Aniseikonia Test; the stereoacuity was evaluated with the Titmus Stereotest. RESULTS: In 41 patients with bilateral PC IOLs, aniseikonia measured with the New Aniseikonia Test ranged from 0% to 4% (mean, 0.76%; standard deviation = 1.04%). The average stereoacuity evaluated with the Titmus test was 7.68 circles (less than 60 seconds; range, greater than 800 to 40 seconds of arc), with 36 of 41 patients (87.8%) showing a stereoacuity less than or equal to 100 seconds of arc. In 37 patients with unilateral PC IOLs, the aniseikonia ranged from 0% to 6% (mean, 0.97%; standard deviation = 1.13%). Their stereoacuity also ranged from greater than 800 to 40 seconds (mean, 7.67 circles) (less than 60 seconds). In this group, 34 of 37 (91.8%) patients showed a stereoacuity less than or equal to 100 seconds of arc. CONCLUSION: Although the problem of aniseikonia still remains, a significant number of patients attain good binocular function after unilateral and bilateral PC IOL implantation.

Adult↗

PubMed1990

Effects of brief monocular deprivation on binocular depth perception in the cat: a sensitive period for the loss of stereopsis.

The period of susceptibility for binocular depth vision was studied in kittens by subjecting them to periods of monocular deprivation beginning at different ages. In an initial study, we found that normally reared kittens can learn a depth-discrimination task much more rapidly when tested binocularly than monocularly, even when testing is begun as early at 30 d. In subsequent experiments, kittens were monocularly deprived by eyelid suture, following which their monocular and binocular depth thresholds were measured using the jumping-stand procedure. We obtained the following results: (1) When monocular deprivation is applied before the time of natural eye opening but is discontinued by no later than 30 d, there is very little effect on binocular depth thresholds. (2) When deprivation is begun at 90 d, binocular depth thresholds are unaffected. (3) When deprivation is begun between these two ages, the magnitude of the deficit varies with the period of deprivation and the age at which it begins. (4) By imposing brief (5 or 10 d) periods of deprivation, beginning at different ages, we were able to demonstrate that the peak of the sensitive period is between the ages of 35 and 45 d, with a fairly rapid decline in susceptibility outside those age limits. (5) Even with as little as 5 d of deprivation, substantial permanent deficits in binocular depth vision can be induced.

Animals↗

PubMed1992

Spatial zones of binocular rivalry in central and peripheral vision.

This paper presents results from psychophysical experiments on human binocular rivalry in central and peripheral vision. Results show that the incidence of periods of exclusive visibility of a given eye's rival target increased with decreasing target size, and for a given sized target exclusive visibility increased with retinal eccentricity. Control measures confirmed that these results were not attributable solely to reduced peripheral acuity, to Troxler's effect, or to spatial frequency. We computed the minimum-sized stimulus that would lead to a criterion level of exclusive visibility of one or the other eye; this we term the spatial zone of binocular rivalry. The change in estimated size of spatial zones of rivalry with eccentricity compares favorably with estimates of human cortical magnification. We propose a model that assumes concentrically organized zones of rivalry. These zones do not function independently, but instead exhibit a high degree of mutual excitatory cooperativity. The model has multiple solutions for the foveal zone size, but the best fits predict a diameter of 5.3 or 7.3 min of visual angle; these values dovetail nicely with our empirical estimates of the foveal zone size.

Humans↗

PubMed1992

Spatial interactions in binocular rivalry.

Observers tracked binocular rivalry between a pair of small, foveally viewed gratings whose orientation differed between the 2 eyes. In Experiment 1, a textured annulus surrounding 1 eye's grating increased the total duration of exclusive visibility of the grating only when the grating-annulus separation was less than 0.5 degree. In Experiment 2, observers tracked the visibility of a monocular annulus that surrounded a foveally viewed grating that was either engaged in rivalry or fused with a grating alone viewed by the other eye. The visibility of the annulus was greater when the grating it surrounded was not undergoing rivalry fluctuations. In Experiment 3, the predominance of a rival grating was greater when the contours in the surrounding annulus were orthogonal to those of the rival grating. In Experiment 4, total exclusive visibility of a given grating-annulus target was greater when the grating and the annulus contained the same orientation.

Adult↗

PubMed1991

[A new simple test for quantitative determination of near aniseikonia].

A quantitative test for the measurement of near distance aniseikonia is presented which is easy to handle. It combines the advantages of the Awaya near distance test with those of the Aulhorn phase difference haploscope: On the one hand the test can easily measure aniseikonia without a large apparatus, on the other hand it allows an exact comparison of the test objects due to the free mobility of the test objects. This is important because of the frequently accompanying motility disorders.

Aniseikonia↗

PubMed1991

[Results of full binocular correction versus conventional methods].

UNLABELLED: 163 patients suffering from different serious troubles were treated with binocular full correction (BFC) i.e. examination by Polatest and prismatic correction. Before, they all had seen other ophthalmologists. The former diagnose and therapy are listed and compared with those of the author. RESULTS: After a 2 2/3 years average follow-up period 68% of the patients were complaintless, 23% felt better. All patients reached at least binocular single vision, although initially 13% had no binocular vision and 1% complained about diplopia. 70% got ideal binocular vision (initially 0%). In the beginning 50 patients suffered from reduced visual acuity. It improved in all cases with differences of v.a. from 2-4/10 to 10/10. From the shown results the author concludes that conventional binocular diagnostic and therapeutic methods do no longer meet the state of the art. It is postulated that BFC should be accepted by school-medicine and that ophthalmologists and orthoptists should be trained in BFC. Only in this way ophthalmologists may fulfil their task to free patients from the many complaints caused by binocular troubles. The used terminology about BFC is explained in the appendix.

Adolescent↗

PubMed1990

[Post-concussion decrease in aniseikonia tolerance].

Besides loss of convergence and accommodation, head injuries can cause fusion deficiency. Part function of sensory fusion is tolerance to sphaerical and meridional aniseikonia. We will present a patient, whose aniseikonia tolerance decreased after a brain concussion.

Aniseikonia↗

PubMed1992

Learning to see random-dot stereograms.

In the present study some specific properties of the learning effects reported for random-dot stereograms are examined. In experiment 1 the retinal position-specific learning effect was reproduced and in a follow-up experiment it was shown that the position specificity of learning can be accounted for by selective visual attention. In experiments 2 and 3 evidence was obtained that suggests that observers can learn, to a certain degree, monocular random-dot patterns and that this learning facilitates the depth percept. This result indicates that the traditional belief that random-dot stereograms are devoid of monocularly recognizable or useful forms should be reconsidered. In the second set of experiments the learning of two binocular surface properties of random-dot stereograms, depth edges and internal depth regions, was investigated. It was shown in experiment 4 that the depth edges of random-dot stereograms are not learned, whereas the results of experiment 5 indicate that the internal depth regions are learned. Finally, in experiment 6 it was shown that depth edges are learned when the internal depth regions of the stereogram are ambiguous. The results are discussed in terms of the importance of the particular type of stimulus used in the learning process and in terms of perceptual learning and attention.

Attention↗

PubMed1992

Mobility of normal observers under conditions of reduced visual input.

The importance in mobility performance of the rate of presentation of visual information, binocular versus monocular vision, the use of multiple rather than single reference points, and local motion parallax was investigated in two experiments. In each experiment ten subjects walked a triangular mobility course in a totally darkened room; the only visible targets were light emitting diodes (LEDs), mounted on poles, at the apices of the triangle. The LEDs were mounted so that one or two could be used in a trial; if two were used the distance between them was varied horizontally (in experiment 1) and vertically (in experiment 2). The subjects walked around the course under a range of conditions, including two 'optimal trials' in full light. The LEDs were flashed for 1 ms at frequencies of 0.5, 1 and 5 Hz in experiment 1 and at 1 and 5 Hz in experiment 2. Mobility was measured with the use of an ultrasonic locator system which measured the subject's position on the course 10 times per second. The mean velocity of the subject in traversing the course was significantly reduced when the flash rate was slower, when the subject had one eye occluded, or when there was only one LED on the pole; when the spacing between the LEDs was varied, either vertically or horizontally performance was unaffected. These results imply that the frequency of updating of visual information is important in determining mobility performance, as are binocular cues, but that local motion parallax is not important. The number of LEDs on each pole had a significant effect on mobility performance an 'object' (two lights) gave more information than a point reference.

Adult↗

PubMed1990

Effect of induced static aniseikonia on fixation performance during oblique gaze.

In a previous study, it was found that oblique gaze and the prismatic effect inherent in dynamic aniseikonia combine to affect the ability to fixate centrally. In the current study, retinal image differences were introduced, whereas prismatic effects were eliminated. This simulates static aniseikonia as opposed to dynamic aniseikonia. At the same time, oblique gaze was simulated by presenting the stimuli in directions other than straight ahead. The directions of presentation contained both horizontal and vertical components. Fixation eccentricity was monitored by using the border enhancement method, as described in previous experiments. It was found that fixation eccentricity increased as the eyes were directed toward stimuli oriented in directions other than straight ahead. When vertical and horizontal components of oblique gaze were combined, the fixation eccentricity was found to be greater than with either component alone. When differential magnification between left and right retinal images was introduced, the fixation eccentricity increased further, the increment being approximately constant for all directions of gaze.

Aniseikonia↗

PubMed1991

Stability of retinal correspondence in normal binocular vision.

Although many studies have suggested absolute stability of retinal correspondence, perhaps more have concluded that the correspondence of adult subjects with normal binocular vision is capable of small variation, particularly with strong sustained demands upon vergence, in order for binocular vision to be maintained. In this comprehensive review of the literature, the reasons for these differences are critically discussed and areas still to be resolved are pointed out.

Depth Perception↗

PubMed1991

Diagnostic occlusion and clinical management of latent hyperphoria.

Occasionally in patients who have symptoms suggestive of a vertical heterophoria no deviation is found, even on careful examination. Six days of occlusion have been recommended for uncovering such "latent" vertical deviations. We investigated prolonged monocular occlusion (Part I) and found that vertical deviations of varying amounts manifested on symptomatic and asymptomatic subjects. Thus, results of prolonged occlusion can be difficult to interpret. Nonadaptive vertical vergence systems have been implicated in development of symptoms. Therefore, it may be that diagnostic monocular occlusion is not appropriate unless patients have symptoms of vertical imbalance. We used (24 h) occlusion and associated phoria measurements (Part II) to determine vertical prism prescriptions which eliminated symptoms of seven symptomatic patients who did not show significant vertical heterophoria on routine clinical testing. We present data and case reports which elucidate the efficacy of this procedure.

Adolescent↗